1. Field of the Invention
The present invention relates to a current signal sensing method for a supplying-end module of an induction type power supply system and a related receiving-end module, and more particularly, to a current signal sensing method capable of detecting current signals in a supplying-end module of an induction type power supply system, in order to use the time difference between currents and driving signals to interpret the load status and existence of metal objects, retrieve modulated signals and data by automatically adjusting voltage levels for triggering the current signals, and retrieve modulated signals and data by interpreting the difference between half-cycle current signals. The present invention also discloses a related receiving-end module.
2. Description of the Prior Art
For safety purposes, a power supply device of an induction type power supply system has to ensure that a proper power receiving device is positioned on the sensing area of a supplying-end coil of the power supply device, and that the power receiving device is ready to receive power before the power is supplied. In order to allow the power supply device to confirm the above conditions, a data code should be transmitted for identification purposes. The data code transmission is performed via the following steps: the power supply device drives the supplying-end coil to generate resonance and sends electromagnetic power to the power receiving device in order to transmit power. When the power receiving device receives the power, the power receiving device may change the impedance on the receiving-end coil via the signal modulation technology, and any variations are fed back to vary the amplitude of carriers on the supplying-end coil. In the prior art, the variations in voltage and current which occur on the amplitude of carriers on the supplying-end coil should be retrieved through a coil voltage detection circuit. The retrieved voltage variations on the carriers (AC signals with a high frequency) should be filtered by a low-pass filter to obtain differential DC signals, and the current variations should also be converted to voltage signals for processing. The variations in these signals are quite small and thus require amplification before the modulated signals are retrieved. U.S. application Ser. No. 14/017,321 uses a signal analysis circuit to perform low-pass filtering and DC voltage level decoupling, and other circuits (e.g. comparators) are incorporated to convert these small variations of the modulated signals into digital signals. The modulated signals are then able to be interpreted and decoded via software in the microprocessor.
The structure of the circuit in the abovementioned prior art has some drawbacks, however. The variations in the voltage and current may not be sufficiently clear and stable. When the signals enter the signal analysis circuit at the back-end, these small signals may not be interpreted if the amplification ratio is too small, or may easily be blended with noise if the amplification ratio is too large. Circuit design is therefore difficult, which causes unreliability. The variations in the voltage and current may be different due to disposition of the coil, magnitude of transmitted power or other reasons. If the transmitted power is increased, the modulation ratio (i.e. the ratio of magnitudes of the resonant carriers and the modulated signals) may be reduced and the difficulty of interpreting the data codes may increase accordingly, such that the signal modulation capability will diminish as it approaches a full-load status. The signals should undergo filtering before being interpreted; hence, the variations in the modulated signals on the carriers require several cycles to pass through the filter. A cycle of the modulated signals should be greater than the time for allowing the signals to pass through the filter and become stable, which limits the speed of data transmission. The prior art is only applicable to signal sensing, and the load status of the coil, such as whether the coil is full-load or whether there is any metal object, cannot be obtained. Finally, the signal analysis circuit requires a large number of electronic elements, which increases the cost. More elements may also induce lower reliability, as the circuit may fail when any one of these elements fails. Thus, there is a need for improvement over the prior art.